C14 Quinolinic acid has been found to be a major precursor of homarine in marine shrimp. Since this acid is not formed to any significant degree from tryptophan, quinolinic acid must be derived from another source. An in vitro system capable of forming homarine from 2-C14-acetate will be utilized to study the biosynthesis of quinolinic acid and the enzymes as well as cofactors involved. The decarboxylation and methylation steps involved in the conversion of quinolinic acid to homarine will be investigated. Labeled homarine will be injected into shrimp to investigate its metabolic fate. A study will be made of the possible occurrence of pyridine carboxylic acids other than nicotinic, picolinic and quinolinic acids in crustacea.